1. Field of the Invention
The present invention relates generally to transmissions and more specifically to bearing arrangements of shaft assemblies within marine transmissions.
2. Discussion of the Related Art
It is a common practice to fabricate marine transmission housings out of aluminum castings to reduce the overall weight of a transmission. Notwithstanding, it is noted that components of transmission shaft assemblies such as, for example, clutch shaft assemblies and their respective bearing arrangements are typically made from steel. However, aluminum has a different coefficient of thermal expansion than steel, whereby components made from aluminum tend to expand to a greater extent than do components made from steel.
Accordingly, within a transmission, shaft assemblies and their bearing arrangements that are made from steel expand relatively less than the aluminum transmission housing components per unit of temperature increase. Such differing material characteristics can present problems when, for example, steel bearings of a bearing arrangement that support a steel shaft assembly are set or seated within opposing aluminum walls of an aluminum transmission housing. That is because when the transmission increases temperature, a distance between the opposing aluminum walls increases to a greater extent than does a length of the steel shaft assembly and distance between the bearings that support the shaft assembly, which are set within the aluminum walls.
Stated another way, a “setting” or clearance value, which is defined between the aluminum wall and respective bearing, increases with increases in temperature. Such additional clearance or increase in bearing setting allows the bearings and the shaft assembly components to axially float such that the shaft experiences a noticeable increase in end-play. This can lead to uneven bearing roller loading and uneven loading of gears that are driven by the shaft assembly, leading to premature wear of the bearings, gears, and/or other components within the transmission that require alignment with a centerline of the shaft.
Numerous attempts have been made to resolve such issues associated with discrepancies in coefficients of thermal expansion between housings and bearings. Most of these attempts include complex assemblies that have thrust washers and/or other components made from polymeric, elastomeric, or various exotic materials. However, components made from such materials can be expensive and wear out more quickly than other transmission components, leading to their own failure or failure of cooperating components.